24,538 research outputs found
Hinting at primary composition using asymmetries in time distributions
Evidence of azimuthal asymmetries in the time structure and signal size have
been found in non-vertical showers at the Pierre Auger Observatory. It has been
previously shown that the asymmetry in time distributions offers a new
possibility for the determination of the mass composition. New studies have
demonstrated that the dependence of the asymmetry parameter in the rise-time
and fall-time distributions with sec(theta) shows a clear peak. Both, the
position of the peak, X_asymax, and the size of the asymmetry at X_asymax are
sensitive to primary mass composition and have a small dependence on energy. In
this paper a study of the discriminating power of the new observables to
separate primary species is presented.Comment: To be published in the Proceedings of 29th International Cosmic Ray
Conference (ICRC 2005), Pune, India, August 3-10, 200
Comment on the Adiabatic Condition
The experimental observation of effects due to Berry's phase in quantum
systems is certainly one of the most impressive demonstrations of the
correctness of the superposition principle in quantum mechanics. Since Berry's
original paper in 1984, the spin 1/2 coupled with rotating external magnetic
field has been one of the most studied models where those phases appear. We
also consider a special case of this soluble model. A detailed analysis of the
coupled differential equations and comparison with exact results teach us why
the usual procedure (of neglecting nondiagonal terms) is mathematically sound.Comment: 9 page
Iron Opacity and the Pulsar of Supernova 1987A
Neutron stars formed in Type II supernovae are likely to be initially
obscured by late-time fallback. Although much of the late-time fallback is
quickly accreted via neutrino cooling, some material remains on the neutron
star, forming an atmosphere which slowly accretes through photon emission. In
this paper, we derive structure equations of the fallback atmosphere and
present results of one-dimensional simulations of that fallback. The atmosphere
remaining after neutrino cooling becomes unimportant (less than the Compton
Eddington limit) is only a fraction of the total mass accreted (10^-8 of the
accreted mass or 10^-9 solar masses.) Recombined iron dominates the opacity in
the outer regions leading to an opacity 1000-10,000 times higher than that of
electron scattering alone. The resultant photon emission of the remnant
atmosphere is limited to 1/1000th the Compton Eddington Luminosity. The
late-time evolution of this system leads to the formation of a photon-driven
wind from the accretion of the inner portion of the atmosphere, leaving, for
most cases, a bare neutron star on timescales shorter than a year. The
degenerate remnant of 1987a may not be a black hole. Instead, the fallback
material may have already accreted or blown off in the accretion-driven wind.
If the neutron star has either a low magnetic field or a low rotational spin
frequency, we would not expect to see the neutron star remnant of 1987a.Comment: 15 pages text + 8 figures, accepted by Ap
Estoque de carbono em Terra Preta do ĂŤndio no MunicĂpio de Iranduba-AM.
O presente trabalho objetivou estimar o estoque de carbono até um metro de profundidade em uma área de TPI de aproximadamente seis hectares
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